The present invention relates to a multi-layer solid golf ball having rebound characteristics as good as a conventional two-piece solid golf ball when hitting at high head speed, and having better rebound characteristics than the conventional two-piece solid golf ball when hitting at low head speed. That is, the present invention relates a multi-layer solid golf ball having such a structure that golfers having low head speed at the time of hitting are not at a disadvantage.
Solid golf balls are classified into two-piece golf ball and one-piece golf ball. The two-piece golf ball is mainly used for round play of amateur golfers. The two-piece golf ball has excellent flight distance, but has hard and poor shot feel. The performance of the two-piece golf ball depends on the head speed at the time of hitting, and the two-piece golf ball typically has long flight distance when hitting at high head speed and has short flight distance when hitting at low head speed. However, since it happens often that a golfer having low head speed at the time of hitting and a golfer having high head speed at the time of hitting are in a same group at a round play, a golf ball that golfers having low head speed at the time of hitting are not at a disadvantage, is required.
It has been attempted to improve the defect of the solid golf ball by various means. As a representative example, multi-piece solid golf balls, such as a three-piece solid golf ball obtained by placing an intermediate layer between a core and a cover of the two-piece solid golf ball (as described in, for example, Japanese Patent Kokai Publication Nos. 244174/1992, 142228/1994 and the like), and a four-piece solid golf ball of which the intermediate layer is formed into two-layer structure (as described in, for example, Japanese Patent Kokai Publication Nos. 266959/1997, 179797/1998, 179798/1998 and the like) are proposed.
In Japanese Patent Kokai Publication Nos. 244174/1992 and 142228/1994, a three-piece solid golf ball comprising a core formed from rubber composition, an intermediate layer and a cover formed from thermoplastic resin is described.
In Japanese Patent Kokai Publication No. 266959/1997, a four-piece solid golf ball comprising a three-layer structured core formed from rubber composition and a cover formed from thermoplastic resin is described, and a main object thereof is to improve a flight distance, shot feel and controllability, particularly shot feel and controllability at approach shot when hitting by an iron club.
In Japanese Patent Kokai Publication No. 179797/1998, a four-piece solid golf ball comprising a core formed from rubber composition, an inner intermediate layer formed from thermoplastic resin, an outer intermediate layer formed from rubber composition and a cover formed from thermoplastic resin is described. In Japanese Patent Kokai Publication No. 179798/1998, a four-piece solid golf ball comprising a core and an inner intermediate layer formed from rubber composition, an outer intermediate layer and a cover formed from thermoplastic resin is described. The two four-piece solid golf balls are designed to increase the launch angle and flight distance.
The multi-piece solid golf ball, when compared with the two-piece golf ball, has better shot feel while maintaining excellent flight performance, because the multi-piece golf ball can accomplish a various of hardness distribution. However, it is not considered that the rebound characteristics depend on the head speed at the time of hitting.
A main object of the present invention is to provide a multi-layer solid golf ball having small impact force and good shot feel at the time of hitting, and having excellent rebound characteristics when hitting at low head speed because the rebound characteristics do not depend on the head speed at the time of hitting.
According to the present invention, the object described above has been accomplished by providing a multi-layer solid golf ball comprising a core composed of an inner layer core, an intermediate layer core formed on the inner layer core and an outer layer core formed on the intermediate layer core, and a cover formed on the core; adjusting a deformation amount of the inner layer core, a two-layer structured core obtained by covering the inner layer core with the intermediate layer core and the core (three-layer structured core) obtained by covering the two-layer structured core with the outer layer core to a specified range; and controlling the deformation amount that the deformation amount of the two-layer structured core is larger than that of the inner layer core and is larger than that of the core. The present invention can provide a multi-layer solid golf ball having small impact force and good shot feel at the time of hitting, and having long flight distance when hitting at low head speed because the rebound characteristics do not depend on the head speed at the time of hitting.
This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.